Isolation of neurosecretory granules containing vasopressin and MSEL-neurophysin from guinea pig neurointermediate pituitary

Neuropeptide families: evolutionary perspectives

Examination of neuropeptide families can provide information about phyletic relationships and evolutionary processes. In this article the oxytocin/vasopressin family, growth hormone releasing factor (GRF) superfamily and the substance P/tachykinin family have been considered in detail because they have been isolated from an extraordinarily diverse array of species from several vertebrate classes and invertebrate phyla. More important is that the nucleotide sequence of mRNA or cDNA encoding many of these peptides has been determined, which has allowed evolutionary distances to be estimated based on the DNA mutation rate. The origin of a given family lies in a primordial gene that arose many millions of years ago, and through time, exon duplication and insertion, gene duplication, point mutation and exon loss, the family developed into the forms that are now recognised. For example, in birds, GRF and pituitary adenylate cyclase activating peptide (PACAP) are encoded by the same gene, which probably arose as a result of exon duplication and tandem insertion of the ancestral GRF gene. In mammals GRF is the sole product on one gene, and PACAP is the product of a gene that also produces PACAP-related peptide (PRP), which is homologous to GRF. Thus it appears that between birds and mammals the GRF/PACAP gene duplicated: exon loss gave rise to the mammalian GRF gene, while mutation led to the formation of the mammalian PRP/PACAP gene. The neuropeptide Y superfamily is considered briefly, as is cionin, which is an invertebrate peptide that is closely related to the mammalian gastrin/cholecystokinin family.

Action of neurohypophysial granule Lys-Arg endopeptidase on synthetic polypeptides comprising the processing sequence of provasopressin-neurophysin

Neurohypophysial granule Ca(2+)-dependent endopeptidases have been allowed to act on synthetic polypeptides derived from the N-terminal sequence of bovine provasopressin-neurophysin, namely vasopressinyl-glycyl-lysyl-arginyl-alanylamide and vasopressinyl-glycyl-lysyl-arginyl-alanyl-methionyl-serinamide+ ++. Membrane-bound enzymes have been used at pH 5.5 for 16 hr at 37 degrees C. Products have been identified by high-pressure liquid chromatography (HPLC) and by mass spectrometry performed on substances isolated by HPLC. With both substrates, vasopressinyl-Gly-Lys-Arg(OH) has been identified as a product confirming the Lys-Arg specificity previously observed on small peptide fluorogenic substrates. Cleavage yields, however, appear low suggesting that some factors are missing, for example a targeting action of the precursor neurophysin domain to the granule membrane.

Processing endopeptidase deficiency in neurohypophysial secretory granules of the diabetes insipidus (Brattleboro) rat

The homozygote Brattleboro rat exhibits a hereditary diabetes insipidus due to a deficiency of vasopressin, the antidiuretic hormone. It has previously been shown that in this animal a single nucleotide deletion in the provasopressin gene leads to a mutant precursor with a C-terminal amino acid sequence different from that of the wild-type. However the N-terminal region including the hormone moiety, the processing signal as well as the first two-thirds of the neurophysin is entirely preserved and absence of maturation has to be explained by an additional cause. We show here that the neurohypophysis of the homozygote Brattleboro rat, in contrast to the adenohypophysis, displays a significant decrease in the Lys-Arg processing endopeptidase activity when compared to the heterozygote or the wild-type Wistar. It is suggested that hypothalamic vasopressinergic neurons of the homozygote Brattleboro rat display a deficiency in the processing enzyme in contrast to the oxytocinergic neurons in which processing of prooxytocin is normal.

A neurosecretory granule Lys-Arg Ca(2+)-dependent endopeptidase putatively involved in prooxytocin and provasopressin processing

A Ca(2+)-dependent endopeptidase cleaving at the carboxyl side of the paired Lys-Arg residues has been found in the neurosecretory granules of the rat neurointermediate pituitary. The specificity pattern on synthetic fluorogenic substrates, the inhibitor profile, the pH optimum of 5.0 and the Ca(2+)-dependence are compatible with an involvement of this enzyme in the prooxytocin and the provasopressin processing within the granules. The enzymatic features of the neurohypophysial granule endopeptidase resemble those of the insulinoma granule type II endopeptidase and suggest that the same Ca(2+)-dependent protease or closely related enzymes could be involved in processing Lys-Arg-containing prohormones in neuroendocrine cells.

Heterologue conversion of amphibian hydrin 2 into vasotocin through bovine granule alpha-amidating enzyme

Abstract Hydrin 2 (vasotocinyl-Gly), found along with vasotocin in the neurohypophysis of frogs and toads but not of other vasotocin-bearers such as birds and reptiles, is believed to act on water permeability of frog skin, whereas vasotocin mainly fulfils the antidiuretic function on the kidney. In order to understand the peculiar regulation of provasotocin differential processing in amphibians, conversion of hydrin 2 into vasotocin has been attempted using bovine pituitary granule alpha-amidating enzyme. Generated vasotocin has pharmacological properties and Chromatographic behaviour in high-performance liquid chromatography identical to those of synthetic vasotocin. However, the low yield of conversion (5% to 10%) suggests that additional factor(s) might be involved in the physiological processing.

Complete amino acid sequence of goose VLDV-neurophysin. Traces of a putative gene conversion between promesotocin and provasotocin genes

Goose VLDV-neurophysin (mesotocin-associated neurophysin) has been purified from posterior pituitary glands through molecular sieving on Sephadex G-75 and high-pressure reverse-phase liquid chromatography on Nucleosil C-18 columns. Despite apparent molecular mass of unreduced VLDV-neurophysin measured by polyacrylamide gel electrophoresis with sodium dodecylsulfate appeared near 17 kDa, this value fell to 11 kDa after reduction with mercaptoethanol, suggesting the existence of a homodimer. Complete amino acid sequence (93 residues) of goose VLDV-neurophysin has been determined. N- and C-terminal sequences of the protein have been established by Edman degradation (microsequencing) and use of carboxypeptidase Y, respectively. Peptides derived from oxidized or carboxamidomethylated neurophysin by trypsin or staphylococcal proteinase hydrolyses have been isolated by high-pressure liquid chromatography and microsequenced, allowing determination of the complete sequence. Comparison within the vertebrate VLDV-neurophysin lineage, namely goose VLDV-neurophysin to mammalian VLDV-neurophysins and to deduced toad VLDV-neurophysin, reveals a residue insertion between positions 66 and 67 in the nonmammalian VLDV-neurophysins. When goose MSEL-neurophysin (vasotocin-associated neurophysin) and goose VLDV-neurophysin are compared to their bovine counterparts, identical substitutions are found in positions 17 (Asn in both goose neurophysins instead of Gly in both ox neurophysins), 18 (Arg instead of Lys), 35 (Tyr instead of Phe), and 41 (Thr instead of Ala). Identity of the sequences 10-74 in both ox neurophysins has been explained by partial gene conversion between oxytocin and vasopressin genes, and identical substitutions in both goose neurophysins might reveal a similar gene conversion between mesotocin and vasopressin genes in birds.

Hydrins, hydroosmotic neurohypophysial peptides: osmoregulatory adaptation in amphibians through vasotocin precursor processing

From neurointermediate pituitary glands of Xenopus laevis and Rana esculenta, previously unreported peptides termed hydrins, active on water permeability of frog urinary bladder and frog skin (Brunn or "water-balance" effect), have been isolated and sequenced. These peptides seem to be derived from the pro-vasotocin-neurophysin precursor. Hydrin 1, found in Xenopus, has been identified as vasotocin C-terminally extended with the Gly-Lys-Arg sequence; hydrin 2, found in Rana, has been identified as vasotocin C-terminally extended with glycine. Hydrin 2 has been detected in several Ranidae (R. esculenta, Rana temporaria, Rana pipiens) and Bufonidae (Bufo bufo, Bufo ictericus) and appears to have a large distribution in terrestrial or semiaquatic anurans. Hydrins, in contrast to vasotocin, are not active on rat uterus or rat blood pressure. They are absent from other vasotocin-bearers such as birds and could be involved specifically in water-electrolyte regulation of amphibians.

Isolation of neurosecretory granules containing vasotocin, mesotocin, MSEL- and VLDV-neurophysins from goose neurohypophysis

Neurosecretory granules have been isolated from goose posterior pituitaries and their contents have been analyzed by reverse-phase high-pressure liquid chromatography and polyacrylamide gel electrophoresis. Vasotocin and mesotocin have been identified by their biological activities and their retention times compared with those of synthetic peptides. MSEL- and VLDV-neurophysins have been characterized by their N-terminal sequences, their electrophoretic migrations and their retention times, compared with those of purified goose neurophysins. In contrast to the two-step processing of mammalian provasopressin, processing of the vasotocin - MSEL-neurophysin precursor appears to involve only one cleavage giving the hormone and a "big" MSEL-neurophysin homologous to mammalian MSEL-neurophysin extended by copeptin.